Amanda Knox was "psychologically tortured" into falsely accusing a bar owner of murdering Meredith Kercher, she has claimed in a lengthy letter sent to a Florence court.

Ms Knox (26), who was convicted but later acquitted of the murder, said she had never been "violent or psychopathic", nor was she a drug addict or "obsessed by sex".

The American sent the five-page letter, written in Italian, to the appeals court in Florence from Seattle, her home town.

She has lived there ever since being acquitted of the murder of the 21-year-old British undergraduate, who was found stabbed to death in Perugia, Umbria, in November 2007.

The court is rehearing the case and could decide to uphold an original guilty verdict against Ms Knox and her Italian former boyfriend, Raffaele Sollecito (29).

Prosecutors have asked for Ms Knox to be sent to jail for 30 years -- four years more than her original conviction, handed down in 2009.

"We have to recognise that a person can be forced to falsely confess by being tortured psychologically," she wrote in the letter, which was read out to the court.

The court is expected to hand down its verdict on January 10 or 15.

She was referring to the fact that in the days after the murder, she was interrogated by police and falsely blamed the crime on Patrick Lumumba, a Congolese bar owner for whom she worked part-time.

He was arrested and imprisoned but subsequently released after being shown to have a firm alibi for the night in question.

Ms Knox said she was subjected to extreme intimidation by police officers who questioned her in a Perugia police station a few days after Ms Kercher was found dead in the hillside cottage she shared with the American and two Italian women.

She again denied that she had killed Ms Kercher, dismissing prosecutors' claims that the murder was fuelled by sexual jealousy and rows over housekeeping and personal hygiene.

"Meredith was my friend. She was kind to me, she helped me, she was generous and fun. She never criticised me. She never gave me so much as a dirty look.